Fruits of citrus such as orange, navels and grapefruit contain sugars and citric acid. Their unique saccharinity (sweetness flavor) is basically the total soluble solids of citrus juice (mainly sucrose and other sugars and usually measured with a Brix hydrometer) divided by the total % of acidity (mainly citric and other organic acids) as calculated by titration with standard alkali. The resulting number is called Ratio. Usually, the Brix/acid ratio is used as an index of the sweetness, of citrus fruits and improvement in their sweetness by lowering the acidity and/or increasing the Brix value which result in an increase in this ratio, is desired.
It is known that an arsenic compound, such as sodium arsanilate or lead arsenate, can be used to increase the sweetness of citrus fruits. The use of arsenic compounds has been prohibited since the spring of 1987 in the United States of America, except for extremely limited use, for example, for grapefruit, because these compounds are considered toxic.